As a symbol, the butterfly represents transformation, ascension, immortality, rebirth and resurrection. It can also be a symbol for the soul.
In Shamanistic tradition too, the butterfly is a sign for (self-)transformation. "It is akin to the air. It is the Mind, and the ability to know the mind or to change it. It is the art of transformation." See "the Medicine Cards" for more practical information on what you can do, when faced with the Butterfly.